The present invention relates to water-insoluble black pigments. In particular, the present invention relates to water-insoluble black pigments produced from a specified water-soluble sulfide dyestuff and amines.
Black pigments are used in quantities in various industrial fields. For example, they are used as a colorant for paint, printing ink, ink for recording materials such as ribbon for dot printers, melt transfer ink or ink for ink-jet printers, a colorant for a toner for electrostatic photography, an infrared absorber, a laser-marking agent and a charge regulator. The black pigments include inorganic and organic pigments such as carbon black, Nigrosine dyestuffs, metal complex dyestuffs and the like.
Among them, carbon black is insoluble in ordinary organic solvents and it, therefore, is usually used in a dispersion state. Carbon black is quite liable to cause aggregation in dispersion state and various contrivances for maintaining the state of dispersion over a long period of time must be carried out. Thus the cost on using carbon black as a black pigment must be inevitably high.
Nigrosine dyestuffs are used in limited fields, since they are soluble in only some solvents and are scarcely dispersible in resins and their fastnesses to light are not enough high. In mutagenicity tests (Ames tests), Nigrosine dyestuffs give positive results in most cases.
Metal complex dyestuffs have some problems that a pure black hue can scarcely be obtained on metal complex dyestuffs and that negative results are scarcely obtained in mutagenicity tests.
Thus, the development of a water-insoluble black pigment having high solubility in ordinary solvents and excellent compatibility with a resin, and exhibiting negative results in mutagenicity tests is demanded.
After intensive investigations made for the purpose of solving the above-described problems, the inventors have completed the present invention.